Coronary artery disease may produce coronary lesions in the blood vessels providing blood to the heart, such as a stenosis (abnormal narrowing of a blood vessel). As a result, blood flow to the heart may be restricted. A patient suffering from coronary artery disease may experience chest pain, referred to as chronic stable angina during physical exertion or unstable angina when the patient is at rest. A more severe manifestation of disease may lead to myocardial infarction, or heart attack.
A need exists to provide more accurate data relating to coronary lesions, e.g., size, shape, location, functional significance (e.g., whether the lesion impacts blood flow), etc. Patients suffering from chest pain and/or exhibiting symptoms of coronary artery disease may be subjected to one or more tests that may provide some indirect evidence relating to coronary lesions. For example, noninvasive tests may include electrocardiograms, biomarker evaluation from blood tests, treadmill tests, echocardiography, single positron emission computed tomography (SPECT), and positron emission tomography (PET). These noninvasive tests, however, typically do not provide a direct assessment of coronary lesions or assess blood flow rates. The noninvasive tests may provide indirect evidence of coronary lesions by looking for changes in electrical activity of the heart (e.g., using electrocardiography (ECG)), motion of the myocardium (e.g., using stress echocardiography), perfusion of the myocardium (e.g., using PET or SPECT), or metabolic changes (e.g., using biomarkers).
For example, anatomic data may be obtained noninvasively using coronary computed tomographic angiography (CCTA). CCTA may be used for imaging of patients with chest pain and involves using computed tomography (CT) technology to image the heart and the coronary arteries following an intravenous infusion of a contrast agent. However, CCTA also cannot provide direct information on the functional significance of coronary lesions, e.g., whether the lesions affect blood flow. In addition, since CCTA is purely a diagnostic test, it cannot be used to predict changes in coronary blood flow, pressure, or myocardial perfusion under other physiologic states, e.g., exercise, nor can it be used to predict outcomes of interventions.
Thus, patients may also require an invasive test, such as diagnostic cardiac catheterization, to visualize coronary lesions. Diagnostic cardiac catheterization may include performing conventional coronary angiography (CCA) to gather anatomic data on coronary lesions by providing a doctor with an image of the size and shape of the arteries. CCA, however, does not provide data for assessing the functional significance of coronary lesions. For example, a doctor may not be able to diagnose whether a coronary lesion is harmful without determining whether the lesion is functionally significant. Thus, CCA has led to what has been referred to as an “oculostenotic reflex” of some interventional cardiologists to insert a stent for every lesion found with CCA regardless of whether the lesion is functionally significant. As a result, CCA may lead to unnecessary operations on the patient, which may pose added risks to patients and may result in unnecessary heath care costs for patients.
During diagnostic cardiac catheterization, the functional significance of a coronary lesion may be assessed invasively by measuring the fractional flow reserve (FFR) of an observed lesion. FFR is defined as the ratio of the mean blood pressure downstream of a lesion divided by the mean blood pressure upstream from the lesion, e.g., the aortic pressure, under conditions of maximally increased coronary blood flow, e.g., induced by intravenous administration of adenosine. The blood pressures may be measured by inserting a pressure wire into the patient. Thus, the decision to treat a lesion based on the determined FFR may be made after the initial cost and risk of diagnostic cardiac catheterization has already been incurred.
Another technique for evaluating a patient's coronary vasculature is the SYNTAX scoring system and method, which is a technique to score the complexity and severity of coronary artery disease. The SYNTAX score is a rating method used to help determine whether patients should be treated with percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG). Standard SYNTAX scoring is performed by evaluating a patient's coronary anatomy via angiograms, answering a series of questions, and assigning point values based on the answers to the questions. For example, a cardiologist may review a patient's angiogram and assign penalty points for lesions based on, for example, each lesion's type, shape, and location in the patient's coronary tree. The assessed points are then added together to output a single SYNTAX score for the patient. In one exemplary embodiment, if the score is less than 34, PCI is appropriate, and if the score is greater than 34, then CABG will more likely produce a better outcome. It has been found that SYNTAX scoring is very effective in evaluating the complexity and extent of disease in a patient's coronary vasculature, and identifying the most appropriate intervention (e.g., PCI vs. CABG). An embodiment of the SYNTAX scoring system is operating at http://www.syntaxscore.com/, which includes a scoring tutorial, vessel segment definitions, and scoring calculator, the entire disclosure of which is incorporated herein by reference.
Despite its significant benefits, SYNTAX scoring is traditionally an invasive technique because it is performed based on angiograms. Moreover, SYNTAX scoring can be a very time consuming process, as it requires cardiologists to manually/visually evaluate angiograms, answer a long series of questions, and assign a score based on each answer. In addition, the results of SYNTAX scoring are cardiologist-dependent, and may vary somewhat based on how one cardiologist perceives and/or scores angiogram images compared to how other cardiologists do so. For this reason, SYNTAX scoring is sometimes performed by several cardiologists, e.g. a three-person panel, so as to generate an average SYNTAX score. However, such a protocol further increases the man-hours involved in generating a useable SYNTAX score. Finally, traditional SYNTAX scoring is usually performed based on a patient's entire coronary vasculature, without regard to any calculated functional result of an identified lesion. For example, a cardiologist may include in a SYNTAX score penalty points for a lesion that does not negatively impact downstream FFR.
Thus, a need exists for systems and methods for assessing coronary anatomy, coronary artery disease, myocardial perfusion, and coronary artery flow noninvasively. In addition, a need exists for noninvasively evaluating the complexity and extent of disease in a patient's coronary vasculature, and identifying the most appropriate intervention (e.g., PCI vs. CABG). In addition, a need exists for evaluating the complexity and extent of disease in a patient's coronary vasculature by automatically performing a numerical evaluation based on noninvasively obtained patient-specific data. A need also exists for systems and methods that incorporate the functional impact of lesions, e.g. based on noninvasive FFR calculation, when performing numerical evaluation of a patient's coronary vasculature.
The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.